struggling to get right boom length

It will between BOOM!
and BOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM! but not as long as BOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOM! I'm sure

Sounds like you (the OP), have a number of physical issues that need a good long time to settle down before you can finish fine-tuning your machine.

You mention moving your cleats back. I note from hanging around on the US ‘Bentrider’ forum that many, (though not all) recumbent riders favour a foot position where the pedal is actually against the arch of the foot, which would affect boom length. This is very different to the favoured upright position where the ball of the foot is used. Most cleat systems, I understand, will not go that far back, so you may find yourself modifying shoes or looking at alternative foot retention systems, if you decide that position might work for you. Searches on ‘Bentrider’ would be a good place to start looking for ideas on these matters.

Thanks for your input @recumbentpanda but I never said I was using cleats, other posters have mentioned cleats, i am currently using toe clips,I have now I think found the sweetspot this morning,
I do have spd's and shoes and will no doubt eventually try them but on my normal bike I found them to be uncomfortable simply because my normal gait is a bit wrong , I have duck feet as in when standing normally my toes are at 10 to 2,and I could not adjust the cleats to suit me.
Thanks to everyone who has offered advice, its appreciated.

Thanks for your input @recumbentpanda but I never said I was using cleats, other posters have mentioned cleats, i am currently using toe clips,I have now I think found the sweetspot this morning,
I do have spd's and shoes and will no doubt eventually try them but on my normal bike I found them to be uncomfortable simply because my normal gait is a bit wrong , I have duck feet as in when standing normally my toes are at 10 to 2,and I could not adjust the cleats to suit me.
Thanks to everyone who has offered advice, its appreciated.

I found setting the pedal a bit shorter than heel on flat of pedal would suggest, try 1cm to begin with and adjust 1/2cm either way until you get it right. The other thing os to set the cleats as far back as you can in the shoe. After I'd done both I've been comfortable for 13 yrs on a variety of recumbents.

Please be careful with just toe clips. The position of your unsupported foot stretched out to your pedal makes gravitational force more likely to pull your foot off the pedal and if it then hits the ground there is a risk of "leg suck" (if on a tadpole trike - not if on a Delta) which can be devastating.

Those that don't like cleat systems often use a combination of toe strap and heel sling.

You can buy SPD cleats that have a higher amount of float (the amount of lateral movement the heel can make freely when clipped in) than standard cleats.

Toestraps worked very well, on an uprigth! On a trike they are very dangerous to say the least, unless they are combined with a heelstrap. I ride on Terra Trike Strapped Heel Support Pedals. I started out with SPD but I never liked them, to locked in position and unable to use the full force of my leg muscles. With the TTSHSP I can move my feat quite a bit and as they are midfoot position I can use the full force of my leg muscles